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  <div class="section" id="transports-and-protocols-callback-based-api">
<h1>18.5.4. Transports and protocols (callback based API)<a class="headerlink" href="#transports-and-protocols-callback-based-api" title="Permalink to this headline">¶</a></h1>
<p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.6/Lib/asyncio/transports.py">Lib/asyncio/transports.py</a></p>
<p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.6/Lib/asyncio/protocols.py">Lib/asyncio/protocols.py</a></p>
<div class="section" id="transports">
<span id="asyncio-transport"></span><h2>18.5.4.1. Transports<a class="headerlink" href="#transports" title="Permalink to this headline">¶</a></h2>
<p>Transports are classes provided by <a class="reference internal" href="asyncio.html#module-asyncio" title="asyncio: Asynchronous I/O, event loop, coroutines and tasks."><code class="xref py py-mod docutils literal"><span class="pre">asyncio</span></code></a> in order to abstract
various kinds of communication channels.  You generally won’t instantiate
a transport yourself; instead, you will call an <a class="reference internal" href="asyncio-eventloop.html#asyncio.AbstractEventLoop" title="asyncio.AbstractEventLoop"><code class="xref py py-class docutils literal"><span class="pre">AbstractEventLoop</span></code></a> method
which will create the transport and try to initiate the underlying
communication channel, calling you back when it succeeds.</p>
<p>Once the communication channel is established, a transport is always
paired with a <a class="reference internal" href="#asyncio-protocol"><span class="std std-ref">protocol</span></a> instance.  The protocol can
then call the transport’s methods for various purposes.</p>
<p><a class="reference internal" href="asyncio.html#module-asyncio" title="asyncio: Asynchronous I/O, event loop, coroutines and tasks."><code class="xref py py-mod docutils literal"><span class="pre">asyncio</span></code></a> currently implements transports for TCP, UDP, SSL, and
subprocess pipes.  The methods available on a transport depend on
the transport’s kind.</p>
<p>The transport classes are <a class="reference internal" href="asyncio-dev.html#asyncio-multithreading"><span class="std std-ref">not thread safe</span></a>.</p>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.6: </span>The socket option <code class="docutils literal"><span class="pre">TCP_NODELAY</span></code> is now set by default.</p>
</div>
<div class="section" id="basetransport">
<h3>18.5.4.1.1. BaseTransport<a class="headerlink" href="#basetransport" title="Permalink to this headline">¶</a></h3>
<dl class="class">
<dt id="asyncio.BaseTransport">
<em class="property">class </em><code class="descclassname">asyncio.</code><code class="descname">BaseTransport</code><a class="headerlink" href="#asyncio.BaseTransport" title="Permalink to this definition">¶</a></dt>
<dd><p>Base class for transports.</p>
<dl class="method">
<dt id="asyncio.BaseTransport.close">
<code class="descname">close</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.BaseTransport.close" title="Permalink to this definition">¶</a></dt>
<dd><p>Close the transport.  If the transport has a buffer for outgoing
data, buffered data will be flushed asynchronously.  No more data
will be received.  After all buffered data is flushed, the
protocol’s <code class="xref py py-meth docutils literal"><span class="pre">connection_lost()</span></code> method will be called with
<a class="reference internal" href="constants.html#None" title="None"><code class="xref py py-const docutils literal"><span class="pre">None</span></code></a> as its argument.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.BaseTransport.is_closing">
<code class="descname">is_closing</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.BaseTransport.is_closing" title="Permalink to this definition">¶</a></dt>
<dd><p>Return <code class="docutils literal"><span class="pre">True</span></code> if the transport is closing or is closed.</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 3.5.1.</span></p>
</div>
</dd></dl>

<dl class="method">
<dt id="asyncio.BaseTransport.get_extra_info">
<code class="descname">get_extra_info</code><span class="sig-paren">(</span><em>name</em>, <em>default=None</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.BaseTransport.get_extra_info" title="Permalink to this definition">¶</a></dt>
<dd><p>Return optional transport information.  <em>name</em> is a string representing
the piece of transport-specific information to get, <em>default</em> is the
value to return if the information doesn’t exist.</p>
<p>This method allows transport implementations to easily expose
channel-specific information.</p>
<ul class="simple">
<li>socket:<ul>
<li><code class="docutils literal"><span class="pre">'peername'</span></code>: the remote address to which the socket is connected,
result of <a class="reference internal" href="socket.html#socket.socket.getpeername" title="socket.socket.getpeername"><code class="xref py py-meth docutils literal"><span class="pre">socket.socket.getpeername()</span></code></a> (<code class="docutils literal"><span class="pre">None</span></code> on error)</li>
<li><code class="docutils literal"><span class="pre">'socket'</span></code>: <a class="reference internal" href="socket.html#socket.socket" title="socket.socket"><code class="xref py py-class docutils literal"><span class="pre">socket.socket</span></code></a> instance</li>
<li><code class="docutils literal"><span class="pre">'sockname'</span></code>: the socket’s own address,
result of <a class="reference internal" href="socket.html#socket.socket.getsockname" title="socket.socket.getsockname"><code class="xref py py-meth docutils literal"><span class="pre">socket.socket.getsockname()</span></code></a></li>
</ul>
</li>
<li>SSL socket:<ul>
<li><code class="docutils literal"><span class="pre">'compression'</span></code>: the compression algorithm being used as a string,
or <code class="docutils literal"><span class="pre">None</span></code> if the connection isn’t compressed; result of
<a class="reference internal" href="ssl.html#ssl.SSLSocket.compression" title="ssl.SSLSocket.compression"><code class="xref py py-meth docutils literal"><span class="pre">ssl.SSLSocket.compression()</span></code></a></li>
<li><code class="docutils literal"><span class="pre">'cipher'</span></code>: a three-value tuple containing the name of the cipher
being used, the version of the SSL protocol that defines its use, and
the number of secret bits being used; result of
<a class="reference internal" href="ssl.html#ssl.SSLSocket.cipher" title="ssl.SSLSocket.cipher"><code class="xref py py-meth docutils literal"><span class="pre">ssl.SSLSocket.cipher()</span></code></a></li>
<li><code class="docutils literal"><span class="pre">'peercert'</span></code>: peer certificate; result of
<a class="reference internal" href="ssl.html#ssl.SSLSocket.getpeercert" title="ssl.SSLSocket.getpeercert"><code class="xref py py-meth docutils literal"><span class="pre">ssl.SSLSocket.getpeercert()</span></code></a></li>
<li><code class="docutils literal"><span class="pre">'sslcontext'</span></code>: <a class="reference internal" href="ssl.html#ssl.SSLContext" title="ssl.SSLContext"><code class="xref py py-class docutils literal"><span class="pre">ssl.SSLContext</span></code></a> instance</li>
<li><code class="docutils literal"><span class="pre">'ssl_object'</span></code>: <a class="reference internal" href="ssl.html#ssl.SSLObject" title="ssl.SSLObject"><code class="xref py py-class docutils literal"><span class="pre">ssl.SSLObject</span></code></a> or <a class="reference internal" href="ssl.html#ssl.SSLSocket" title="ssl.SSLSocket"><code class="xref py py-class docutils literal"><span class="pre">ssl.SSLSocket</span></code></a>
instance</li>
</ul>
</li>
<li>pipe:<ul>
<li><code class="docutils literal"><span class="pre">'pipe'</span></code>: pipe object</li>
</ul>
</li>
<li>subprocess:<ul>
<li><code class="docutils literal"><span class="pre">'subprocess'</span></code>: <a class="reference internal" href="subprocess.html#subprocess.Popen" title="subprocess.Popen"><code class="xref py py-class docutils literal"><span class="pre">subprocess.Popen</span></code></a> instance</li>
</ul>
</li>
</ul>
</dd></dl>

<dl class="method">
<dt id="asyncio.BaseTransport.set_protocol">
<code class="descname">set_protocol</code><span class="sig-paren">(</span><em>protocol</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.BaseTransport.set_protocol" title="Permalink to this definition">¶</a></dt>
<dd><p>Set a new protocol.  Switching protocol should only be done when both
protocols are documented to support the switch.</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 3.5.3.</span></p>
</div>
</dd></dl>

<dl class="method">
<dt id="asyncio.BaseTransport.get_protocol">
<code class="descname">get_protocol</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.BaseTransport.get_protocol" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the current protocol.</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 3.5.3.</span></p>
</div>
</dd></dl>

<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.5.1: </span><code class="docutils literal"><span class="pre">'ssl_object'</span></code> info was added to SSL sockets.</p>
</div>
</dd></dl>

</div>
<div class="section" id="readtransport">
<h3>18.5.4.1.2. ReadTransport<a class="headerlink" href="#readtransport" title="Permalink to this headline">¶</a></h3>
<dl class="class">
<dt id="asyncio.ReadTransport">
<em class="property">class </em><code class="descclassname">asyncio.</code><code class="descname">ReadTransport</code><a class="headerlink" href="#asyncio.ReadTransport" title="Permalink to this definition">¶</a></dt>
<dd><p>Interface for read-only transports.</p>
<dl class="method">
<dt id="asyncio.ReadTransport.pause_reading">
<code class="descname">pause_reading</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.ReadTransport.pause_reading" title="Permalink to this definition">¶</a></dt>
<dd><p>Pause the receiving end of the transport.  No data will be passed to
the protocol’s <code class="xref py py-meth docutils literal"><span class="pre">data_received()</span></code> method until <a class="reference internal" href="#asyncio.ReadTransport.resume_reading" title="asyncio.ReadTransport.resume_reading"><code class="xref py py-meth docutils literal"><span class="pre">resume_reading()</span></code></a>
is called.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.ReadTransport.resume_reading">
<code class="descname">resume_reading</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.ReadTransport.resume_reading" title="Permalink to this definition">¶</a></dt>
<dd><p>Resume the receiving end.  The protocol’s <code class="xref py py-meth docutils literal"><span class="pre">data_received()</span></code> method
will be called once again if some data is available for reading.</p>
</dd></dl>

</dd></dl>

</div>
<div class="section" id="writetransport">
<h3>18.5.4.1.3. WriteTransport<a class="headerlink" href="#writetransport" title="Permalink to this headline">¶</a></h3>
<dl class="class">
<dt id="asyncio.WriteTransport">
<em class="property">class </em><code class="descclassname">asyncio.</code><code class="descname">WriteTransport</code><a class="headerlink" href="#asyncio.WriteTransport" title="Permalink to this definition">¶</a></dt>
<dd><p>Interface for write-only transports.</p>
<dl class="method">
<dt id="asyncio.WriteTransport.abort">
<code class="descname">abort</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.WriteTransport.abort" title="Permalink to this definition">¶</a></dt>
<dd><p>Close the transport immediately, without waiting for pending operations
to complete.  Buffered data will be lost.  No more data will be received.
The protocol’s <code class="xref py py-meth docutils literal"><span class="pre">connection_lost()</span></code> method will eventually be
called with <a class="reference internal" href="constants.html#None" title="None"><code class="xref py py-const docutils literal"><span class="pre">None</span></code></a> as its argument.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.WriteTransport.can_write_eof">
<code class="descname">can_write_eof</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.WriteTransport.can_write_eof" title="Permalink to this definition">¶</a></dt>
<dd><p>Return <a class="reference internal" href="constants.html#True" title="True"><code class="xref py py-const docutils literal"><span class="pre">True</span></code></a> if the transport supports <a class="reference internal" href="#asyncio.WriteTransport.write_eof" title="asyncio.WriteTransport.write_eof"><code class="xref py py-meth docutils literal"><span class="pre">write_eof()</span></code></a>,
<a class="reference internal" href="constants.html#False" title="False"><code class="xref py py-const docutils literal"><span class="pre">False</span></code></a> if not.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.WriteTransport.get_write_buffer_size">
<code class="descname">get_write_buffer_size</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.WriteTransport.get_write_buffer_size" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the current size of the output buffer used by the transport.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.WriteTransport.get_write_buffer_limits">
<code class="descname">get_write_buffer_limits</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.WriteTransport.get_write_buffer_limits" title="Permalink to this definition">¶</a></dt>
<dd><p>Get the <em>high</em>- and <em>low</em>-water limits for write flow control. Return a
tuple <code class="docutils literal"><span class="pre">(low,</span> <span class="pre">high)</span></code> where <em>low</em> and <em>high</em> are positive number of
bytes.</p>
<p>Use <a class="reference internal" href="#asyncio.WriteTransport.set_write_buffer_limits" title="asyncio.WriteTransport.set_write_buffer_limits"><code class="xref py py-meth docutils literal"><span class="pre">set_write_buffer_limits()</span></code></a> to set the limits.</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 3.4.2.</span></p>
</div>
</dd></dl>

<dl class="method">
<dt id="asyncio.WriteTransport.set_write_buffer_limits">
<code class="descname">set_write_buffer_limits</code><span class="sig-paren">(</span><em>high=None</em>, <em>low=None</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.WriteTransport.set_write_buffer_limits" title="Permalink to this definition">¶</a></dt>
<dd><p>Set the <em>high</em>- and <em>low</em>-water limits for write flow control.</p>
<p>These two values (measured in number of
bytes) control when the protocol’s
<code class="xref py py-meth docutils literal"><span class="pre">pause_writing()</span></code> and <code class="xref py py-meth docutils literal"><span class="pre">resume_writing()</span></code> methods are called.
If specified, the low-water limit must be less than or equal to the
high-water limit.  Neither <em>high</em> nor <em>low</em> can be negative.</p>
<p><code class="xref py py-meth docutils literal"><span class="pre">pause_writing()</span></code> is called when the buffer size becomes greater
than or equal to the <em>high</em> value. If writing has been paused,
<code class="xref py py-meth docutils literal"><span class="pre">resume_writing()</span></code> is called when the buffer size becomes less
than or equal to the <em>low</em> value.</p>
<p>The defaults are implementation-specific.  If only the
high-water limit is given, the low-water limit defaults to an
implementation-specific value less than or equal to the
high-water limit.  Setting <em>high</em> to zero forces <em>low</em> to zero as
well, and causes <code class="xref py py-meth docutils literal"><span class="pre">pause_writing()</span></code> to be called whenever the
buffer becomes non-empty.  Setting <em>low</em> to zero causes
<code class="xref py py-meth docutils literal"><span class="pre">resume_writing()</span></code> to be called only once the buffer is empty.
Use of zero for either limit is generally sub-optimal as it
reduces opportunities for doing I/O and computation
concurrently.</p>
<p>Use <a class="reference internal" href="#asyncio.WriteTransport.get_write_buffer_limits" title="asyncio.WriteTransport.get_write_buffer_limits"><code class="xref py py-meth docutils literal"><span class="pre">get_write_buffer_limits()</span></code></a> to get the limits.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.WriteTransport.write">
<code class="descname">write</code><span class="sig-paren">(</span><em>data</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.WriteTransport.write" title="Permalink to this definition">¶</a></dt>
<dd><p>Write some <em>data</em> bytes to the transport.</p>
<p>This method does not block; it buffers the data and arranges for it
to be sent out asynchronously.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.WriteTransport.writelines">
<code class="descname">writelines</code><span class="sig-paren">(</span><em>list_of_data</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.WriteTransport.writelines" title="Permalink to this definition">¶</a></dt>
<dd><p>Write a list (or any iterable) of data bytes to the transport.
This is functionally equivalent to calling <a class="reference internal" href="#asyncio.WriteTransport.write" title="asyncio.WriteTransport.write"><code class="xref py py-meth docutils literal"><span class="pre">write()</span></code></a> on each
element yielded by the iterable, but may be implemented more efficiently.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.WriteTransport.write_eof">
<code class="descname">write_eof</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.WriteTransport.write_eof" title="Permalink to this definition">¶</a></dt>
<dd><p>Close the write end of the transport after flushing buffered data.
Data may still be received.</p>
<p>This method can raise <a class="reference internal" href="exceptions.html#NotImplementedError" title="NotImplementedError"><code class="xref py py-exc docutils literal"><span class="pre">NotImplementedError</span></code></a> if the transport
(e.g. SSL) doesn’t support half-closes.</p>
</dd></dl>

</dd></dl>

</div>
<div class="section" id="datagramtransport">
<h3>18.5.4.1.4. DatagramTransport<a class="headerlink" href="#datagramtransport" title="Permalink to this headline">¶</a></h3>
<dl class="method">
<dt id="asyncio.DatagramTransport.sendto">
<code class="descclassname">DatagramTransport.</code><code class="descname">sendto</code><span class="sig-paren">(</span><em>data</em>, <em>addr=None</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.DatagramTransport.sendto" title="Permalink to this definition">¶</a></dt>
<dd><p>Send the <em>data</em> bytes to the remote peer given by <em>addr</em> (a
transport-dependent target address).  If <em>addr</em> is <a class="reference internal" href="constants.html#None" title="None"><code class="xref py py-const docutils literal"><span class="pre">None</span></code></a>, the
data is sent to the target address given on transport creation.</p>
<p>This method does not block; it buffers the data and arranges for it
to be sent out asynchronously.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.DatagramTransport.abort">
<code class="descclassname">DatagramTransport.</code><code class="descname">abort</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.DatagramTransport.abort" title="Permalink to this definition">¶</a></dt>
<dd><p>Close the transport immediately, without waiting for pending operations
to complete.  Buffered data will be lost.  No more data will be received.
The protocol’s <code class="xref py py-meth docutils literal"><span class="pre">connection_lost()</span></code> method will eventually be
called with <a class="reference internal" href="constants.html#None" title="None"><code class="xref py py-const docutils literal"><span class="pre">None</span></code></a> as its argument.</p>
</dd></dl>

</div>
<div class="section" id="basesubprocesstransport">
<h3>18.5.4.1.5. BaseSubprocessTransport<a class="headerlink" href="#basesubprocesstransport" title="Permalink to this headline">¶</a></h3>
<dl class="class">
<dt id="asyncio.BaseSubprocessTransport">
<em class="property">class </em><code class="descclassname">asyncio.</code><code class="descname">BaseSubprocessTransport</code><a class="headerlink" href="#asyncio.BaseSubprocessTransport" title="Permalink to this definition">¶</a></dt>
<dd><dl class="method">
<dt id="asyncio.BaseSubprocessTransport.get_pid">
<code class="descname">get_pid</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.BaseSubprocessTransport.get_pid" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the subprocess process id as an integer.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.BaseSubprocessTransport.get_pipe_transport">
<code class="descname">get_pipe_transport</code><span class="sig-paren">(</span><em>fd</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.BaseSubprocessTransport.get_pipe_transport" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the transport for the communication pipe corresponding to the
integer file descriptor <em>fd</em>:</p>
<ul class="simple">
<li><code class="docutils literal"><span class="pre">0</span></code>: readable streaming transport of the standard input (<em>stdin</em>),
or <a class="reference internal" href="constants.html#None" title="None"><code class="xref py py-const docutils literal"><span class="pre">None</span></code></a> if the subprocess was not created with <code class="docutils literal"><span class="pre">stdin=PIPE</span></code></li>
<li><code class="docutils literal"><span class="pre">1</span></code>: writable streaming transport of the standard output (<em>stdout</em>),
or <a class="reference internal" href="constants.html#None" title="None"><code class="xref py py-const docutils literal"><span class="pre">None</span></code></a> if the subprocess was not created with <code class="docutils literal"><span class="pre">stdout=PIPE</span></code></li>
<li><code class="docutils literal"><span class="pre">2</span></code>: writable streaming transport of the standard error (<em>stderr</em>),
or <a class="reference internal" href="constants.html#None" title="None"><code class="xref py py-const docutils literal"><span class="pre">None</span></code></a> if the subprocess was not created with <code class="docutils literal"><span class="pre">stderr=PIPE</span></code></li>
<li>other <em>fd</em>: <a class="reference internal" href="constants.html#None" title="None"><code class="xref py py-const docutils literal"><span class="pre">None</span></code></a></li>
</ul>
</dd></dl>

<dl class="method">
<dt id="asyncio.BaseSubprocessTransport.get_returncode">
<code class="descname">get_returncode</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.BaseSubprocessTransport.get_returncode" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the subprocess returncode as an integer or <a class="reference internal" href="constants.html#None" title="None"><code class="xref py py-const docutils literal"><span class="pre">None</span></code></a>
if it hasn’t returned, similarly to the
<a class="reference internal" href="subprocess.html#subprocess.Popen.returncode" title="subprocess.Popen.returncode"><code class="xref py py-attr docutils literal"><span class="pre">subprocess.Popen.returncode</span></code></a> attribute.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.BaseSubprocessTransport.kill">
<code class="descname">kill</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.BaseSubprocessTransport.kill" title="Permalink to this definition">¶</a></dt>
<dd><p>Kill the subprocess, as in <a class="reference internal" href="subprocess.html#subprocess.Popen.kill" title="subprocess.Popen.kill"><code class="xref py py-meth docutils literal"><span class="pre">subprocess.Popen.kill()</span></code></a>.</p>
<p>On POSIX systems, the function sends SIGKILL to the subprocess.
On Windows, this method is an alias for <a class="reference internal" href="#asyncio.BaseSubprocessTransport.terminate" title="asyncio.BaseSubprocessTransport.terminate"><code class="xref py py-meth docutils literal"><span class="pre">terminate()</span></code></a>.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.BaseSubprocessTransport.send_signal">
<code class="descname">send_signal</code><span class="sig-paren">(</span><em>signal</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.BaseSubprocessTransport.send_signal" title="Permalink to this definition">¶</a></dt>
<dd><p>Send the <em>signal</em> number to the subprocess, as in
<a class="reference internal" href="subprocess.html#subprocess.Popen.send_signal" title="subprocess.Popen.send_signal"><code class="xref py py-meth docutils literal"><span class="pre">subprocess.Popen.send_signal()</span></code></a>.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.BaseSubprocessTransport.terminate">
<code class="descname">terminate</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.BaseSubprocessTransport.terminate" title="Permalink to this definition">¶</a></dt>
<dd><p>Ask the subprocess to stop, as in <a class="reference internal" href="subprocess.html#subprocess.Popen.terminate" title="subprocess.Popen.terminate"><code class="xref py py-meth docutils literal"><span class="pre">subprocess.Popen.terminate()</span></code></a>.
This method is an alias for the <a class="reference internal" href="#asyncio.BaseSubprocessTransport.close" title="asyncio.BaseSubprocessTransport.close"><code class="xref py py-meth docutils literal"><span class="pre">close()</span></code></a> method.</p>
<p>On POSIX systems, this method sends SIGTERM to the subprocess.
On Windows, the Windows API function TerminateProcess() is called to
stop the subprocess.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.BaseSubprocessTransport.close">
<code class="descname">close</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.BaseSubprocessTransport.close" title="Permalink to this definition">¶</a></dt>
<dd><p>Ask the subprocess to stop by calling the <a class="reference internal" href="#asyncio.BaseSubprocessTransport.terminate" title="asyncio.BaseSubprocessTransport.terminate"><code class="xref py py-meth docutils literal"><span class="pre">terminate()</span></code></a> method if the
subprocess hasn’t returned yet, and close transports of all pipes
(<em>stdin</em>, <em>stdout</em> and <em>stderr</em>).</p>
</dd></dl>

</dd></dl>

</div>
</div>
<div class="section" id="protocols">
<span id="asyncio-protocol"></span><h2>18.5.4.2. Protocols<a class="headerlink" href="#protocols" title="Permalink to this headline">¶</a></h2>
<p><a class="reference internal" href="asyncio.html#module-asyncio" title="asyncio: Asynchronous I/O, event loop, coroutines and tasks."><code class="xref py py-mod docutils literal"><span class="pre">asyncio</span></code></a> provides base classes that you can subclass to implement
your network protocols.  Those classes are used in conjunction with
<a class="reference internal" href="#asyncio-transport"><span class="std std-ref">transports</span></a> (see below): the protocol parses incoming
data and asks for the writing of outgoing data, while the transport is
responsible for the actual I/O and buffering.</p>
<p>When subclassing a protocol class, it is recommended you override certain
methods.  Those methods are callbacks: they will be called by the transport
on certain events (for example when some data is received); you shouldn’t
call them yourself, unless you are implementing a transport.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">All callbacks have default implementations, which are empty.  Therefore,
you only need to implement the callbacks for the events in which you
are interested.</p>
</div>
<div class="section" id="protocol-classes">
<h3>18.5.4.2.1. Protocol classes<a class="headerlink" href="#protocol-classes" title="Permalink to this headline">¶</a></h3>
<dl class="class">
<dt id="asyncio.Protocol">
<em class="property">class </em><code class="descclassname">asyncio.</code><code class="descname">Protocol</code><a class="headerlink" href="#asyncio.Protocol" title="Permalink to this definition">¶</a></dt>
<dd><p>The base class for implementing streaming protocols (for use with
e.g. TCP and SSL transports).</p>
</dd></dl>

<dl class="class">
<dt id="asyncio.DatagramProtocol">
<em class="property">class </em><code class="descclassname">asyncio.</code><code class="descname">DatagramProtocol</code><a class="headerlink" href="#asyncio.DatagramProtocol" title="Permalink to this definition">¶</a></dt>
<dd><p>The base class for implementing datagram protocols (for use with
e.g. UDP transports).</p>
</dd></dl>

<dl class="class">
<dt id="asyncio.SubprocessProtocol">
<em class="property">class </em><code class="descclassname">asyncio.</code><code class="descname">SubprocessProtocol</code><a class="headerlink" href="#asyncio.SubprocessProtocol" title="Permalink to this definition">¶</a></dt>
<dd><p>The base class for implementing protocols communicating with child
processes (through a set of unidirectional pipes).</p>
</dd></dl>

</div>
<div class="section" id="connection-callbacks">
<h3>18.5.4.2.2. Connection callbacks<a class="headerlink" href="#connection-callbacks" title="Permalink to this headline">¶</a></h3>
<p>These callbacks may be called on <a class="reference internal" href="#asyncio.Protocol" title="asyncio.Protocol"><code class="xref py py-class docutils literal"><span class="pre">Protocol</span></code></a>, <a class="reference internal" href="#asyncio.DatagramProtocol" title="asyncio.DatagramProtocol"><code class="xref py py-class docutils literal"><span class="pre">DatagramProtocol</span></code></a>
and <a class="reference internal" href="#asyncio.SubprocessProtocol" title="asyncio.SubprocessProtocol"><code class="xref py py-class docutils literal"><span class="pre">SubprocessProtocol</span></code></a> instances:</p>
<dl class="method">
<dt id="asyncio.BaseProtocol.connection_made">
<code class="descclassname">BaseProtocol.</code><code class="descname">connection_made</code><span class="sig-paren">(</span><em>transport</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.BaseProtocol.connection_made" title="Permalink to this definition">¶</a></dt>
<dd><p>Called when a connection is made.</p>
<p>The <em>transport</em> argument is the transport representing the
connection.  You are responsible for storing it somewhere
(e.g. as an attribute) if you need to.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.BaseProtocol.connection_lost">
<code class="descclassname">BaseProtocol.</code><code class="descname">connection_lost</code><span class="sig-paren">(</span><em>exc</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.BaseProtocol.connection_lost" title="Permalink to this definition">¶</a></dt>
<dd><p>Called when the connection is lost or closed.</p>
<p>The argument is either an exception object or <a class="reference internal" href="constants.html#None" title="None"><code class="xref py py-const docutils literal"><span class="pre">None</span></code></a>.
The latter means a regular EOF is received, or the connection was
aborted or closed by this side of the connection.</p>
</dd></dl>

<p><a class="reference internal" href="#asyncio.BaseProtocol.connection_made" title="asyncio.BaseProtocol.connection_made"><code class="xref py py-meth docutils literal"><span class="pre">connection_made()</span></code></a> and <a class="reference internal" href="#asyncio.BaseProtocol.connection_lost" title="asyncio.BaseProtocol.connection_lost"><code class="xref py py-meth docutils literal"><span class="pre">connection_lost()</span></code></a>
are called exactly once per successful connection.  All other callbacks will be
called between those two methods, which allows for easier resource management
in your protocol implementation.</p>
<p>The following callbacks may be called only on <a class="reference internal" href="#asyncio.SubprocessProtocol" title="asyncio.SubprocessProtocol"><code class="xref py py-class docutils literal"><span class="pre">SubprocessProtocol</span></code></a>
instances:</p>
<dl class="method">
<dt id="asyncio.SubprocessProtocol.pipe_data_received">
<code class="descclassname">SubprocessProtocol.</code><code class="descname">pipe_data_received</code><span class="sig-paren">(</span><em>fd</em>, <em>data</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.SubprocessProtocol.pipe_data_received" title="Permalink to this definition">¶</a></dt>
<dd><p>Called when the child process writes data into its stdout or stderr pipe.
<em>fd</em> is the integer file descriptor of the pipe.  <em>data</em> is a non-empty
bytes object containing the data.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.SubprocessProtocol.pipe_connection_lost">
<code class="descclassname">SubprocessProtocol.</code><code class="descname">pipe_connection_lost</code><span class="sig-paren">(</span><em>fd</em>, <em>exc</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.SubprocessProtocol.pipe_connection_lost" title="Permalink to this definition">¶</a></dt>
<dd><p>Called when one of the pipes communicating with the child process
is closed.  <em>fd</em> is the integer file descriptor that was closed.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.SubprocessProtocol.process_exited">
<code class="descclassname">SubprocessProtocol.</code><code class="descname">process_exited</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.SubprocessProtocol.process_exited" title="Permalink to this definition">¶</a></dt>
<dd><p>Called when the child process has exited.</p>
</dd></dl>

</div>
<div class="section" id="streaming-protocols">
<h3>18.5.4.2.3. Streaming protocols<a class="headerlink" href="#streaming-protocols" title="Permalink to this headline">¶</a></h3>
<p>The following callbacks are called on <a class="reference internal" href="#asyncio.Protocol" title="asyncio.Protocol"><code class="xref py py-class docutils literal"><span class="pre">Protocol</span></code></a> instances:</p>
<dl class="method">
<dt id="asyncio.Protocol.data_received">
<code class="descclassname">Protocol.</code><code class="descname">data_received</code><span class="sig-paren">(</span><em>data</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Protocol.data_received" title="Permalink to this definition">¶</a></dt>
<dd><p>Called when some data is received.  <em>data</em> is a non-empty bytes object
containing the incoming data.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">Whether the data is buffered, chunked or reassembled depends on
the transport.  In general, you shouldn’t rely on specific semantics
and instead make your parsing generic and flexible enough.  However,
data is always received in the correct order.</p>
</div>
</dd></dl>

<dl class="method">
<dt id="asyncio.Protocol.eof_received">
<code class="descclassname">Protocol.</code><code class="descname">eof_received</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Protocol.eof_received" title="Permalink to this definition">¶</a></dt>
<dd><p>Called when the other end signals it won’t send any more data
(for example by calling <code class="xref py py-meth docutils literal"><span class="pre">write_eof()</span></code>, if the other end also uses
asyncio).</p>
<p>This method may return a false value (including <code class="docutils literal"><span class="pre">None</span></code>), in which case
the transport will close itself.  Conversely, if this method returns a
true value, closing the transport is up to the protocol.  Since the
default implementation returns <code class="docutils literal"><span class="pre">None</span></code>, it implicitly closes the connection.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">Some transports such as SSL don’t support half-closed connections,
in which case returning true from this method will not prevent closing
the connection.</p>
</div>
</dd></dl>

<p><code class="xref py py-meth docutils literal"><span class="pre">data_received()</span></code> can be called an arbitrary number of times during
a connection.  However, <code class="xref py py-meth docutils literal"><span class="pre">eof_received()</span></code> is called at most once
and, if called, <code class="xref py py-meth docutils literal"><span class="pre">data_received()</span></code> won’t be called after it.</p>
<p>State machine:</p>
<blockquote>
<div>start -&gt; <a class="reference internal" href="#asyncio.BaseProtocol.connection_made" title="asyncio.BaseProtocol.connection_made"><code class="xref py py-meth docutils literal"><span class="pre">connection_made()</span></code></a>
[-&gt; <a class="reference internal" href="#asyncio.Protocol.data_received" title="asyncio.Protocol.data_received"><code class="xref py py-meth docutils literal"><span class="pre">data_received()</span></code></a> *]
[-&gt; <a class="reference internal" href="#asyncio.Protocol.eof_received" title="asyncio.Protocol.eof_received"><code class="xref py py-meth docutils literal"><span class="pre">eof_received()</span></code></a> ?]
-&gt; <a class="reference internal" href="#asyncio.BaseProtocol.connection_lost" title="asyncio.BaseProtocol.connection_lost"><code class="xref py py-meth docutils literal"><span class="pre">connection_lost()</span></code></a> -&gt; end</div></blockquote>
</div>
<div class="section" id="datagram-protocols">
<h3>18.5.4.2.4. Datagram protocols<a class="headerlink" href="#datagram-protocols" title="Permalink to this headline">¶</a></h3>
<p>The following callbacks are called on <a class="reference internal" href="#asyncio.DatagramProtocol" title="asyncio.DatagramProtocol"><code class="xref py py-class docutils literal"><span class="pre">DatagramProtocol</span></code></a> instances.</p>
<dl class="method">
<dt id="asyncio.DatagramProtocol.datagram_received">
<code class="descclassname">DatagramProtocol.</code><code class="descname">datagram_received</code><span class="sig-paren">(</span><em>data</em>, <em>addr</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.DatagramProtocol.datagram_received" title="Permalink to this definition">¶</a></dt>
<dd><p>Called when a datagram is received.  <em>data</em> is a bytes object containing
the incoming data.  <em>addr</em> is the address of the peer sending the data;
the exact format depends on the transport.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.DatagramProtocol.error_received">
<code class="descclassname">DatagramProtocol.</code><code class="descname">error_received</code><span class="sig-paren">(</span><em>exc</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.DatagramProtocol.error_received" title="Permalink to this definition">¶</a></dt>
<dd><p>Called when a previous send or receive operation raises an
<a class="reference internal" href="exceptions.html#OSError" title="OSError"><code class="xref py py-class docutils literal"><span class="pre">OSError</span></code></a>.  <em>exc</em> is the <a class="reference internal" href="exceptions.html#OSError" title="OSError"><code class="xref py py-class docutils literal"><span class="pre">OSError</span></code></a> instance.</p>
<p>This method is called in rare conditions, when the transport (e.g. UDP)
detects that a datagram couldn’t be delivered to its recipient.
In many conditions though, undeliverable datagrams will be silently
dropped.</p>
</dd></dl>

</div>
<div class="section" id="flow-control-callbacks">
<h3>18.5.4.2.5. Flow control callbacks<a class="headerlink" href="#flow-control-callbacks" title="Permalink to this headline">¶</a></h3>
<p>These callbacks may be called on <a class="reference internal" href="#asyncio.Protocol" title="asyncio.Protocol"><code class="xref py py-class docutils literal"><span class="pre">Protocol</span></code></a>,
<a class="reference internal" href="#asyncio.DatagramProtocol" title="asyncio.DatagramProtocol"><code class="xref py py-class docutils literal"><span class="pre">DatagramProtocol</span></code></a> and <a class="reference internal" href="#asyncio.SubprocessProtocol" title="asyncio.SubprocessProtocol"><code class="xref py py-class docutils literal"><span class="pre">SubprocessProtocol</span></code></a> instances:</p>
<dl class="method">
<dt id="asyncio.BaseProtocol.pause_writing">
<code class="descclassname">BaseProtocol.</code><code class="descname">pause_writing</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.BaseProtocol.pause_writing" title="Permalink to this definition">¶</a></dt>
<dd><p>Called when the transport’s buffer goes over the high-water mark.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.BaseProtocol.resume_writing">
<code class="descclassname">BaseProtocol.</code><code class="descname">resume_writing</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.BaseProtocol.resume_writing" title="Permalink to this definition">¶</a></dt>
<dd><p>Called when the transport’s buffer drains below the low-water mark.</p>
</dd></dl>

<p><code class="xref py py-meth docutils literal"><span class="pre">pause_writing()</span></code> and <code class="xref py py-meth docutils literal"><span class="pre">resume_writing()</span></code> calls are paired –
<code class="xref py py-meth docutils literal"><span class="pre">pause_writing()</span></code> is called once when the buffer goes strictly over
the high-water mark (even if subsequent writes increases the buffer size
even more), and eventually <code class="xref py py-meth docutils literal"><span class="pre">resume_writing()</span></code> is called once when the
buffer size reaches the low-water mark.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">If the buffer size equals the high-water mark,
<code class="xref py py-meth docutils literal"><span class="pre">pause_writing()</span></code> is not called – it must go strictly over.
Conversely, <code class="xref py py-meth docutils literal"><span class="pre">resume_writing()</span></code> is called when the buffer size is
equal or lower than the low-water mark.  These end conditions
are important to ensure that things go as expected when either
mark is zero.</p>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">On BSD systems (OS X, FreeBSD, etc.) flow control is not supported
for <a class="reference internal" href="#asyncio.DatagramProtocol" title="asyncio.DatagramProtocol"><code class="xref py py-class docutils literal"><span class="pre">DatagramProtocol</span></code></a>, because send failures caused by
writing too many packets cannot be detected easily.  The socket
always appears ‘ready’ and excess packets are dropped; an
<a class="reference internal" href="exceptions.html#OSError" title="OSError"><code class="xref py py-class docutils literal"><span class="pre">OSError</span></code></a> with errno set to <a class="reference internal" href="errno.html#errno.ENOBUFS" title="errno.ENOBUFS"><code class="xref py py-const docutils literal"><span class="pre">errno.ENOBUFS</span></code></a> may or
may not be raised; if it is raised, it will be reported to
<a class="reference internal" href="#asyncio.DatagramProtocol.error_received" title="asyncio.DatagramProtocol.error_received"><code class="xref py py-meth docutils literal"><span class="pre">DatagramProtocol.error_received()</span></code></a> but otherwise ignored.</p>
</div>
</div>
<div class="section" id="coroutines-and-protocols">
<h3>18.5.4.2.6. Coroutines and protocols<a class="headerlink" href="#coroutines-and-protocols" title="Permalink to this headline">¶</a></h3>
<p>Coroutines can be scheduled in a protocol method using <a class="reference internal" href="asyncio-task.html#asyncio.ensure_future" title="asyncio.ensure_future"><code class="xref py py-func docutils literal"><span class="pre">ensure_future()</span></code></a>,
but there is no guarantee made about the execution order.  Protocols are not
aware of coroutines created in protocol methods and so will not wait for them.</p>
<p>To have a reliable execution order, use <a class="reference internal" href="asyncio-stream.html#asyncio-streams"><span class="std std-ref">stream objects</span></a> in a
coroutine with <code class="docutils literal"><span class="pre">yield</span> <span class="pre">from</span></code>. For example, the <a class="reference internal" href="asyncio-stream.html#asyncio.StreamWriter.drain" title="asyncio.StreamWriter.drain"><code class="xref py py-meth docutils literal"><span class="pre">StreamWriter.drain()</span></code></a>
coroutine can be used to wait until the write buffer is flushed.</p>
</div>
</div>
<div class="section" id="protocol-examples">
<h2>18.5.4.3. Protocol examples<a class="headerlink" href="#protocol-examples" title="Permalink to this headline">¶</a></h2>
<div class="section" id="tcp-echo-client-protocol">
<span id="asyncio-tcp-echo-client-protocol"></span><h3>18.5.4.3.1. TCP echo client protocol<a class="headerlink" href="#tcp-echo-client-protocol" title="Permalink to this headline">¶</a></h3>
<p>TCP echo client  using the <a class="reference internal" href="asyncio-eventloop.html#asyncio.AbstractEventLoop.create_connection" title="asyncio.AbstractEventLoop.create_connection"><code class="xref py py-meth docutils literal"><span class="pre">AbstractEventLoop.create_connection()</span></code></a> method, send
data and wait until the connection is closed:</p>
<div class="highlight-python3"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">asyncio</span>

<span class="k">class</span> <span class="nc">EchoClientProtocol</span><span class="p">(</span><span class="n">asyncio</span><span class="o">.</span><span class="n">Protocol</span><span class="p">):</span>
    <span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">message</span><span class="p">,</span> <span class="n">loop</span><span class="p">):</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">message</span> <span class="o">=</span> <span class="n">message</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">loop</span> <span class="o">=</span> <span class="n">loop</span>

    <span class="k">def</span> <span class="nf">connection_made</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">transport</span><span class="p">):</span>
        <span class="n">transport</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">message</span><span class="o">.</span><span class="n">encode</span><span class="p">())</span>
        <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;Data sent: </span><span class="si">{!r}</span><span class="s1">&#39;</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">message</span><span class="p">))</span>

    <span class="k">def</span> <span class="nf">data_received</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">data</span><span class="p">):</span>
        <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;Data received: </span><span class="si">{!r}</span><span class="s1">&#39;</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="n">data</span><span class="o">.</span><span class="n">decode</span><span class="p">()))</span>

    <span class="k">def</span> <span class="nf">connection_lost</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">exc</span><span class="p">):</span>
        <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;The server closed the connection&#39;</span><span class="p">)</span>
        <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;Stop the event loop&#39;</span><span class="p">)</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">loop</span><span class="o">.</span><span class="n">stop</span><span class="p">()</span>

<span class="n">loop</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">get_event_loop</span><span class="p">()</span>
<span class="n">message</span> <span class="o">=</span> <span class="s1">&#39;Hello World!&#39;</span>
<span class="n">coro</span> <span class="o">=</span> <span class="n">loop</span><span class="o">.</span><span class="n">create_connection</span><span class="p">(</span><span class="k">lambda</span><span class="p">:</span> <span class="n">EchoClientProtocol</span><span class="p">(</span><span class="n">message</span><span class="p">,</span> <span class="n">loop</span><span class="p">),</span>
                              <span class="s1">&#39;127.0.0.1&#39;</span><span class="p">,</span> <span class="mi">8888</span><span class="p">)</span>
<span class="n">loop</span><span class="o">.</span><span class="n">run_until_complete</span><span class="p">(</span><span class="n">coro</span><span class="p">)</span>
<span class="n">loop</span><span class="o">.</span><span class="n">run_forever</span><span class="p">()</span>
<span class="n">loop</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
</pre></div>
</div>
<p>The event loop is running twice. The
<a class="reference internal" href="asyncio-eventloop.html#asyncio.AbstractEventLoop.run_until_complete" title="asyncio.AbstractEventLoop.run_until_complete"><code class="xref py py-meth docutils literal"><span class="pre">run_until_complete()</span></code></a> method is preferred in this short
example to raise an exception if the server is not listening, instead of
having to write a short coroutine to handle the exception and stop the
running loop. At <a class="reference internal" href="asyncio-eventloop.html#asyncio.AbstractEventLoop.run_until_complete" title="asyncio.AbstractEventLoop.run_until_complete"><code class="xref py py-meth docutils literal"><span class="pre">run_until_complete()</span></code></a> exit, the loop is
no longer running, so there is no need to stop the loop in case of an error.</p>
<div class="admonition seealso">
<p class="first admonition-title">See also</p>
<p class="last">The <a class="reference internal" href="asyncio-stream.html#asyncio-tcp-echo-client-streams"><span class="std std-ref">TCP echo client using streams</span></a>
example uses the <a class="reference internal" href="asyncio-stream.html#asyncio.open_connection" title="asyncio.open_connection"><code class="xref py py-func docutils literal"><span class="pre">asyncio.open_connection()</span></code></a> function.</p>
</div>
</div>
<div class="section" id="tcp-echo-server-protocol">
<span id="asyncio-tcp-echo-server-protocol"></span><h3>18.5.4.3.2. TCP echo server protocol<a class="headerlink" href="#tcp-echo-server-protocol" title="Permalink to this headline">¶</a></h3>
<p>TCP echo server using the <a class="reference internal" href="asyncio-eventloop.html#asyncio.AbstractEventLoop.create_server" title="asyncio.AbstractEventLoop.create_server"><code class="xref py py-meth docutils literal"><span class="pre">AbstractEventLoop.create_server()</span></code></a> method, send back
received data and close the connection:</p>
<div class="highlight-python3"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">asyncio</span>

<span class="k">class</span> <span class="nc">EchoServerClientProtocol</span><span class="p">(</span><span class="n">asyncio</span><span class="o">.</span><span class="n">Protocol</span><span class="p">):</span>
    <span class="k">def</span> <span class="nf">connection_made</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">transport</span><span class="p">):</span>
        <span class="n">peername</span> <span class="o">=</span> <span class="n">transport</span><span class="o">.</span><span class="n">get_extra_info</span><span class="p">(</span><span class="s1">&#39;peername&#39;</span><span class="p">)</span>
        <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;Connection from </span><span class="si">{}</span><span class="s1">&#39;</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="n">peername</span><span class="p">))</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">transport</span> <span class="o">=</span> <span class="n">transport</span>

    <span class="k">def</span> <span class="nf">data_received</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">data</span><span class="p">):</span>
        <span class="n">message</span> <span class="o">=</span> <span class="n">data</span><span class="o">.</span><span class="n">decode</span><span class="p">()</span>
        <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;Data received: </span><span class="si">{!r}</span><span class="s1">&#39;</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="n">message</span><span class="p">))</span>

        <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;Send: </span><span class="si">{!r}</span><span class="s1">&#39;</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="n">message</span><span class="p">))</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">transport</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="n">data</span><span class="p">)</span>

        <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;Close the client socket&#39;</span><span class="p">)</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">transport</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>

<span class="n">loop</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">get_event_loop</span><span class="p">()</span>
<span class="c1"># Each client connection will create a new protocol instance</span>
<span class="n">coro</span> <span class="o">=</span> <span class="n">loop</span><span class="o">.</span><span class="n">create_server</span><span class="p">(</span><span class="n">EchoServerClientProtocol</span><span class="p">,</span> <span class="s1">&#39;127.0.0.1&#39;</span><span class="p">,</span> <span class="mi">8888</span><span class="p">)</span>
<span class="n">server</span> <span class="o">=</span> <span class="n">loop</span><span class="o">.</span><span class="n">run_until_complete</span><span class="p">(</span><span class="n">coro</span><span class="p">)</span>

<span class="c1"># Serve requests until Ctrl+C is pressed</span>
<span class="nb">print</span><span class="p">(</span><span class="s1">&#39;Serving on </span><span class="si">{}</span><span class="s1">&#39;</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="n">server</span><span class="o">.</span><span class="n">sockets</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="o">.</span><span class="n">getsockname</span><span class="p">()))</span>
<span class="k">try</span><span class="p">:</span>
    <span class="n">loop</span><span class="o">.</span><span class="n">run_forever</span><span class="p">()</span>
<span class="k">except</span> <span class="ne">KeyboardInterrupt</span><span class="p">:</span>
    <span class="k">pass</span>

<span class="c1"># Close the server</span>
<span class="n">server</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
<span class="n">loop</span><span class="o">.</span><span class="n">run_until_complete</span><span class="p">(</span><span class="n">server</span><span class="o">.</span><span class="n">wait_closed</span><span class="p">())</span>
<span class="n">loop</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
</pre></div>
</div>
<p><code class="xref py py-meth docutils literal"><span class="pre">Transport.close()</span></code> can be called immediately after
<a class="reference internal" href="#asyncio.WriteTransport.write" title="asyncio.WriteTransport.write"><code class="xref py py-meth docutils literal"><span class="pre">WriteTransport.write()</span></code></a> even if data are not sent yet on the socket: both
methods are asynchronous. <code class="docutils literal"><span class="pre">yield</span> <span class="pre">from</span></code> is not needed because these transport
methods are not coroutines.</p>
<div class="admonition seealso">
<p class="first admonition-title">See also</p>
<p class="last">The <a class="reference internal" href="asyncio-stream.html#asyncio-tcp-echo-server-streams"><span class="std std-ref">TCP echo server using streams</span></a>
example uses the <a class="reference internal" href="asyncio-stream.html#asyncio.start_server" title="asyncio.start_server"><code class="xref py py-func docutils literal"><span class="pre">asyncio.start_server()</span></code></a> function.</p>
</div>
</div>
<div class="section" id="udp-echo-client-protocol">
<span id="asyncio-udp-echo-client-protocol"></span><h3>18.5.4.3.3. UDP echo client protocol<a class="headerlink" href="#udp-echo-client-protocol" title="Permalink to this headline">¶</a></h3>
<p>UDP echo client using the <a class="reference internal" href="asyncio-eventloop.html#asyncio.AbstractEventLoop.create_datagram_endpoint" title="asyncio.AbstractEventLoop.create_datagram_endpoint"><code class="xref py py-meth docutils literal"><span class="pre">AbstractEventLoop.create_datagram_endpoint()</span></code></a>
method, send data and close the transport when we received the answer:</p>
<div class="highlight-python3"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">asyncio</span>

<span class="k">class</span> <span class="nc">EchoClientProtocol</span><span class="p">:</span>
    <span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">message</span><span class="p">,</span> <span class="n">loop</span><span class="p">):</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">message</span> <span class="o">=</span> <span class="n">message</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">loop</span> <span class="o">=</span> <span class="n">loop</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">transport</span> <span class="o">=</span> <span class="kc">None</span>

    <span class="k">def</span> <span class="nf">connection_made</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">transport</span><span class="p">):</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">transport</span> <span class="o">=</span> <span class="n">transport</span>
        <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;Send:&#39;</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">message</span><span class="p">)</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">transport</span><span class="o">.</span><span class="n">sendto</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">message</span><span class="o">.</span><span class="n">encode</span><span class="p">())</span>

    <span class="k">def</span> <span class="nf">datagram_received</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">data</span><span class="p">,</span> <span class="n">addr</span><span class="p">):</span>
        <span class="nb">print</span><span class="p">(</span><span class="s2">&quot;Received:&quot;</span><span class="p">,</span> <span class="n">data</span><span class="o">.</span><span class="n">decode</span><span class="p">())</span>

        <span class="nb">print</span><span class="p">(</span><span class="s2">&quot;Close the socket&quot;</span><span class="p">)</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">transport</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>

    <span class="k">def</span> <span class="nf">error_received</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">exc</span><span class="p">):</span>
        <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;Error received:&#39;</span><span class="p">,</span> <span class="n">exc</span><span class="p">)</span>

    <span class="k">def</span> <span class="nf">connection_lost</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">exc</span><span class="p">):</span>
        <span class="nb">print</span><span class="p">(</span><span class="s2">&quot;Socket closed, stop the event loop&quot;</span><span class="p">)</span>
        <span class="n">loop</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">get_event_loop</span><span class="p">()</span>
        <span class="n">loop</span><span class="o">.</span><span class="n">stop</span><span class="p">()</span>

<span class="n">loop</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">get_event_loop</span><span class="p">()</span>
<span class="n">message</span> <span class="o">=</span> <span class="s2">&quot;Hello World!&quot;</span>
<span class="n">connect</span> <span class="o">=</span> <span class="n">loop</span><span class="o">.</span><span class="n">create_datagram_endpoint</span><span class="p">(</span>
    <span class="k">lambda</span><span class="p">:</span> <span class="n">EchoClientProtocol</span><span class="p">(</span><span class="n">message</span><span class="p">,</span> <span class="n">loop</span><span class="p">),</span>
    <span class="n">remote_addr</span><span class="o">=</span><span class="p">(</span><span class="s1">&#39;127.0.0.1&#39;</span><span class="p">,</span> <span class="mi">9999</span><span class="p">))</span>
<span class="n">transport</span><span class="p">,</span> <span class="n">protocol</span> <span class="o">=</span> <span class="n">loop</span><span class="o">.</span><span class="n">run_until_complete</span><span class="p">(</span><span class="n">connect</span><span class="p">)</span>
<span class="n">loop</span><span class="o">.</span><span class="n">run_forever</span><span class="p">()</span>
<span class="n">transport</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
<span class="n">loop</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
</pre></div>
</div>
</div>
<div class="section" id="udp-echo-server-protocol">
<span id="asyncio-udp-echo-server-protocol"></span><h3>18.5.4.3.4. UDP echo server protocol<a class="headerlink" href="#udp-echo-server-protocol" title="Permalink to this headline">¶</a></h3>
<p>UDP echo server using the <a class="reference internal" href="asyncio-eventloop.html#asyncio.AbstractEventLoop.create_datagram_endpoint" title="asyncio.AbstractEventLoop.create_datagram_endpoint"><code class="xref py py-meth docutils literal"><span class="pre">AbstractEventLoop.create_datagram_endpoint()</span></code></a>
method, send back received data:</p>
<div class="highlight-python3"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">asyncio</span>

<span class="k">class</span> <span class="nc">EchoServerProtocol</span><span class="p">:</span>
    <span class="k">def</span> <span class="nf">connection_made</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">transport</span><span class="p">):</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">transport</span> <span class="o">=</span> <span class="n">transport</span>

    <span class="k">def</span> <span class="nf">datagram_received</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">data</span><span class="p">,</span> <span class="n">addr</span><span class="p">):</span>
        <span class="n">message</span> <span class="o">=</span> <span class="n">data</span><span class="o">.</span><span class="n">decode</span><span class="p">()</span>
        <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;Received </span><span class="si">%r</span><span class="s1"> from </span><span class="si">%s</span><span class="s1">&#39;</span> <span class="o">%</span> <span class="p">(</span><span class="n">message</span><span class="p">,</span> <span class="n">addr</span><span class="p">))</span>
        <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;Send </span><span class="si">%r</span><span class="s1"> to </span><span class="si">%s</span><span class="s1">&#39;</span> <span class="o">%</span> <span class="p">(</span><span class="n">message</span><span class="p">,</span> <span class="n">addr</span><span class="p">))</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">transport</span><span class="o">.</span><span class="n">sendto</span><span class="p">(</span><span class="n">data</span><span class="p">,</span> <span class="n">addr</span><span class="p">)</span>

<span class="n">loop</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">get_event_loop</span><span class="p">()</span>
<span class="nb">print</span><span class="p">(</span><span class="s2">&quot;Starting UDP server&quot;</span><span class="p">)</span>
<span class="c1"># One protocol instance will be created to serve all client requests</span>
<span class="n">listen</span> <span class="o">=</span> <span class="n">loop</span><span class="o">.</span><span class="n">create_datagram_endpoint</span><span class="p">(</span>
    <span class="n">EchoServerProtocol</span><span class="p">,</span> <span class="n">local_addr</span><span class="o">=</span><span class="p">(</span><span class="s1">&#39;127.0.0.1&#39;</span><span class="p">,</span> <span class="mi">9999</span><span class="p">))</span>
<span class="n">transport</span><span class="p">,</span> <span class="n">protocol</span> <span class="o">=</span> <span class="n">loop</span><span class="o">.</span><span class="n">run_until_complete</span><span class="p">(</span><span class="n">listen</span><span class="p">)</span>

<span class="k">try</span><span class="p">:</span>
    <span class="n">loop</span><span class="o">.</span><span class="n">run_forever</span><span class="p">()</span>
<span class="k">except</span> <span class="ne">KeyboardInterrupt</span><span class="p">:</span>
    <span class="k">pass</span>

<span class="n">transport</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
<span class="n">loop</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
</pre></div>
</div>
</div>
<div class="section" id="register-an-open-socket-to-wait-for-data-using-a-protocol">
<span id="asyncio-register-socket"></span><h3>18.5.4.3.5. Register an open socket to wait for data using a protocol<a class="headerlink" href="#register-an-open-socket-to-wait-for-data-using-a-protocol" title="Permalink to this headline">¶</a></h3>
<p>Wait until a socket receives data using the
<a class="reference internal" href="asyncio-eventloop.html#asyncio.AbstractEventLoop.create_connection" title="asyncio.AbstractEventLoop.create_connection"><code class="xref py py-meth docutils literal"><span class="pre">AbstractEventLoop.create_connection()</span></code></a> method with a protocol, and then close
the event loop</p>
<div class="highlight-python3"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">asyncio</span>
<span class="k">try</span><span class="p">:</span>
    <span class="kn">from</span> <span class="nn">socket</span> <span class="k">import</span> <span class="n">socketpair</span>
<span class="k">except</span> <span class="ne">ImportError</span><span class="p">:</span>
    <span class="kn">from</span> <span class="nn">asyncio.windows_utils</span> <span class="k">import</span> <span class="n">socketpair</span>

<span class="c1"># Create a pair of connected sockets</span>
<span class="n">rsock</span><span class="p">,</span> <span class="n">wsock</span> <span class="o">=</span> <span class="n">socketpair</span><span class="p">()</span>
<span class="n">loop</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">get_event_loop</span><span class="p">()</span>

<span class="k">class</span> <span class="nc">MyProtocol</span><span class="p">(</span><span class="n">asyncio</span><span class="o">.</span><span class="n">Protocol</span><span class="p">):</span>
    <span class="n">transport</span> <span class="o">=</span> <span class="kc">None</span>

    <span class="k">def</span> <span class="nf">connection_made</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">transport</span><span class="p">):</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">transport</span> <span class="o">=</span> <span class="n">transport</span>

    <span class="k">def</span> <span class="nf">data_received</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">data</span><span class="p">):</span>
        <span class="nb">print</span><span class="p">(</span><span class="s2">&quot;Received:&quot;</span><span class="p">,</span> <span class="n">data</span><span class="o">.</span><span class="n">decode</span><span class="p">())</span>

        <span class="c1"># We are done: close the transport (it will call connection_lost())</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">transport</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>

    <span class="k">def</span> <span class="nf">connection_lost</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">exc</span><span class="p">):</span>
        <span class="c1"># The socket has been closed, stop the event loop</span>
        <span class="n">loop</span><span class="o">.</span><span class="n">stop</span><span class="p">()</span>

<span class="c1"># Register the socket to wait for data</span>
<span class="n">connect_coro</span> <span class="o">=</span> <span class="n">loop</span><span class="o">.</span><span class="n">create_connection</span><span class="p">(</span><span class="n">MyProtocol</span><span class="p">,</span> <span class="n">sock</span><span class="o">=</span><span class="n">rsock</span><span class="p">)</span>
<span class="n">transport</span><span class="p">,</span> <span class="n">protocol</span> <span class="o">=</span> <span class="n">loop</span><span class="o">.</span><span class="n">run_until_complete</span><span class="p">(</span><span class="n">connect_coro</span><span class="p">)</span>

<span class="c1"># Simulate the reception of data from the network</span>
<span class="n">loop</span><span class="o">.</span><span class="n">call_soon</span><span class="p">(</span><span class="n">wsock</span><span class="o">.</span><span class="n">send</span><span class="p">,</span> <span class="s1">&#39;abc&#39;</span><span class="o">.</span><span class="n">encode</span><span class="p">())</span>

<span class="c1"># Run the event loop</span>
<span class="n">loop</span><span class="o">.</span><span class="n">run_forever</span><span class="p">()</span>

<span class="c1"># We are done, close sockets and the event loop</span>
<span class="n">rsock</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
<span class="n">wsock</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
<span class="n">loop</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
</pre></div>
</div>
<div class="admonition seealso">
<p class="first admonition-title">See also</p>
<p>The <a class="reference internal" href="asyncio-eventloop.html#asyncio-watch-read-event"><span class="std std-ref">watch a file descriptor for read events</span></a> example uses the low-level
<a class="reference internal" href="asyncio-eventloop.html#asyncio.AbstractEventLoop.add_reader" title="asyncio.AbstractEventLoop.add_reader"><code class="xref py py-meth docutils literal"><span class="pre">AbstractEventLoop.add_reader()</span></code></a> method to register the file descriptor of a
socket.</p>
<p class="last">The <a class="reference internal" href="asyncio-stream.html#asyncio-register-socket-streams"><span class="std std-ref">register an open socket to wait for data using streams</span></a> example uses high-level streams
created by the <a class="reference internal" href="asyncio-stream.html#asyncio.open_connection" title="asyncio.open_connection"><code class="xref py py-func docutils literal"><span class="pre">open_connection()</span></code></a> function in a coroutine.</p>
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  <ul>
<li><a class="reference internal" href="#">18.5.4. Transports and protocols (callback based API)</a><ul>
<li><a class="reference internal" href="#transports">18.5.4.1. Transports</a><ul>
<li><a class="reference internal" href="#basetransport">18.5.4.1.1. BaseTransport</a></li>
<li><a class="reference internal" href="#readtransport">18.5.4.1.2. ReadTransport</a></li>
<li><a class="reference internal" href="#writetransport">18.5.4.1.3. WriteTransport</a></li>
<li><a class="reference internal" href="#datagramtransport">18.5.4.1.4. DatagramTransport</a></li>
<li><a class="reference internal" href="#basesubprocesstransport">18.5.4.1.5. BaseSubprocessTransport</a></li>
</ul>
</li>
<li><a class="reference internal" href="#protocols">18.5.4.2. Protocols</a><ul>
<li><a class="reference internal" href="#protocol-classes">18.5.4.2.1. Protocol classes</a></li>
<li><a class="reference internal" href="#connection-callbacks">18.5.4.2.2. Connection callbacks</a></li>
<li><a class="reference internal" href="#streaming-protocols">18.5.4.2.3. Streaming protocols</a></li>
<li><a class="reference internal" href="#datagram-protocols">18.5.4.2.4. Datagram protocols</a></li>
<li><a class="reference internal" href="#flow-control-callbacks">18.5.4.2.5. Flow control callbacks</a></li>
<li><a class="reference internal" href="#coroutines-and-protocols">18.5.4.2.6. Coroutines and protocols</a></li>
</ul>
</li>
<li><a class="reference internal" href="#protocol-examples">18.5.4.3. Protocol examples</a><ul>
<li><a class="reference internal" href="#tcp-echo-client-protocol">18.5.4.3.1. TCP echo client protocol</a></li>
<li><a class="reference internal" href="#tcp-echo-server-protocol">18.5.4.3.2. TCP echo server protocol</a></li>
<li><a class="reference internal" href="#udp-echo-client-protocol">18.5.4.3.3. UDP echo client protocol</a></li>
<li><a class="reference internal" href="#udp-echo-server-protocol">18.5.4.3.4. UDP echo server protocol</a></li>
<li><a class="reference internal" href="#register-an-open-socket-to-wait-for-data-using-a-protocol">18.5.4.3.5. Register an open socket to wait for data using a protocol</a></li>
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